The present invention relates to non-silver photosensitive compositions. More particularly, it relates to such compositions comprising, as components, certain aromatic amines and nitrate ester type chain polymers, which components co-react on suitable exposure to ultraviolet light, thereby sufficiently altering the physical properties of the composition to either directly yield a visible and useful image or, with lesser required exposure, be simply and easily developed and fixed to useful images, including compositions useful in direct service as photoresists.
The admixture of small amounts of certain aromatic amines with smokeless powder nitrocellulose has been variously suggested for stabilizing the powder against degradation effects ("Cellulose and Cellulose Derivatives", E. Ott, p 643 Interscience Publishers, 1943). The development of color upon subsequent oxidation of the amines is not a factor in such service.
The oxidation of aromatic amines to form dyes and colorants is old and widely practiced art ("The Chemistry of Synthetic Dyes", K. Verkataraman, especially pp 767-779, Academic Press, 1952). Many oxidants, including nitric acid and its decomposition products, have been employed.
It was also previously known that organic polyhalogen compounds could be combined with aryl amines in photosensitive compositions, wherein the organic polyhalogen compounds were activated by visible or ultraviolet light to generate free radicals, which reacted with the aryl amines to form colored products. See, e.g. Kosar, "Light Sensitive Systems", pp 361-380 (1965); U.S. Pat. no. 3,042,515 to Eugene Wainer. In such systems, the polyhalogen compound and amine were generally encompassed within a plastic film former or base of some sort. The polyhalogen compounds, in addition to providing a material which is photolytically activated to react with the aryl amine to form the colored products, may also form coordination compounds with certain amines, which coordination compounds may themselves further photolytically react. The effect of the ability to form coordination compounds is to extend the photolytic sensitivity of the composition to longer wavelengths of light.
There are a wide variety of plastics which have been used as the binder in systems such as Wainer's. Wainer preferred that the base material be a hydrogen donor (i.e., reducing agent), in which case the overall color-forming reaction was postulated by Wainer as one in which the polyhalogen compound is photolytically activated to form free radicals, in the presence of which the plastic base gives up free hydrogen radicals, with the halogen adding to the amine side chain and the hydrogen of alkyl groups produced adding either to the aryl nucleus or to the plastic base. See U.S. Pat. No. 3,042,515, the disclosure of which is hereby incorporated by reference, especially columns 2-3.
Not all of the plastic binders used have been hydrogen donors even though such materials have been preferred. In fact, a large number of other materials, which are not normally so classified, have been used, including commercially available cellulose polymers, such as ethyl cellulose, cellulose acetate and cellulose nitrate.
Thus, while not preferred, there have been photoreactive systems containing certain aromatic amines, a photoactivatable polyhalogen compound, and a cellulose nitrate binder. However, so far as we are aware, in all prior compounds where a nitrate ester polymer such as nitrocellulose is suggested or used as a component of photooxidation imaging systems, including those in which copresent amines are photooxidized to a color, e.g., as in Wainer, it serves solely as an inert substrate or binder, the photooxidation being accomplished by other, more readily activated ingredients such as the halo compounds of Wainer. Thus nowhere is it indicated that the color or course of the reaction differs when nitrocellulose is used as the binder in such systems.
It has also been known to form solvent soluble esters of cellulose by using organic acids, all or part of which contain unsaturated carbon linkages of a type adapted to photoinduce crosslinking, e.g., cinnamic acid, for service as a conventional photocrosslinkable photoresist polymer coating.
Apart from prior knowledge in the field of photographic or photoimaging compositions, the chemistry of photoinitiated reactions between monomeric compounds having nitrate ester groups with certain diphenylamines was studied in Hayward et al., "Photolysis of Nitrate Esters, Part I. Photonitration of Diphenylamine", Canadian Journal of Chemistry, 40, pp 434-440 (1962). That paper indicates that ultraviolet photon absorption by diphenylamine peaks at 285 nm and extends to 335 nm, but that model nitrate ester compounds with ring structure comparable with cellulose do not absorb above 240 nm. Hence, though impurities or local sites of degradation reactions, etc. may make a nitrocellulose absorb longer wavelengths somewhat, the nitrate ester groups of nitrocellulose are not photoactivated by wavelengths above 240 nm either. Howard et al. state that mixtures of diphenylamine and their monomeric nitrate ester compounds do develop color on prolonged exposure to ultraviolet wavelengths which are not absorbable by the nitrate esters but are absorbable by diphenylamine. Their work concerns possible uses in chemical manufacture and contains no suggestion either of possible photographic or imaging applications or of using nitrate ester polymers such as nitrocellulose.